There has been considerable interest in recent years in developing methods for reducing lactose levels in milk and milk-derived products. This interest has been heightened by recent evidence that a large percentage of the human population suffers from a lactase deficiency which is either an inherited trait or a result of the aging process. Such lactase deficiencies lead to intestinal disorders when dietary levels of lactose are high. Moreover, a similar lactose intolerance has also been observed in certain domestic animals.
The hydrolysis of lactose in milk and milk-derived products to product glucose and galactose is an attractive goal not only because it would solve the lactose intolerance problem but it would also increase the sweetness of the products and reduce so-called sandy textures in certain milk-derived products caused by lactose crystallization. Those working in the field have long appreciated the desirability of effecting this hydrolysis by the use of lactase. In spite of the fact that lactase occurs rather widely in nature and is produced by many microorganisms, the use of lactase in the commercial production of milk and milk-derived products has been very limited. One reason for the limited commercial use of lactase is that many of the common lactases such as those derived from yeast exhibit optimum enzyme activity at temperatures which are also conducive to bacterial growth. Accordingly, there has been increasing interest in finding a lactase having a high degree of heat stability. Such a heat stable lactase would permit lactose hydrolysis to be carried out under conditions that are unfavorable for growth of certain bacteria which are commonly present in milk or milk-derived products. One such lactase derived from Streptomyces coelicolor has recently been described in U.S. Pat. No. 3,816,259. It is not clear at this time, however, whether lactase from S. coelicolor can be used with impunity because certain members of that species have been reported to produce antibiotics.
The production of lactase by members of the genus Bacillus has been previously reported. P. J. Anema has reported in Biochim. Biophys. Acta 89 (3), 495-502 (1964) the isolation of lactase from B. subtilis. Lactase from B. megaterium was described by S. R. Rohlfing and I. P. Crawford in J. Bacteriology 92 (4), 1258-9 (1966). Neither of these organisms, however, is regarded as heat-tolerant and the lactase produced by them must generally be used at temperatures below about 50.degree. C. in order to retain useful enzyme activity for extended periods of time.